Acid containing monomers are commonly used in acrylic pressure-sensitive adhesives (PSAs) to increase cohesive properties via cross-linking. Their use, however, has been limited to low to moderate concentrations, i.e., 10% or less, since high acid levels lead to an adverse increase in the glass transition temperature and storage modulus to a point where the polymers begin to lose their PSA properties.
Several patents, each of which is incorporated herein by reference, disclose the use of acrylic polymers of high carboxylic acid content to increase cohesive strength.
U.S. Pat. No. 4,404,246 describes the use of 10 to 25% acrylic acid, methacrylic acid, or itaconic acid in combination with a lower alkoxylated amino formaldehyde as a latent cross-linking agent. The compositions are uncross-linked prior to heating which induces cure leading to high peel and shear, especially at elevated temperatures.
U.S. Pat. No. 4,737,410 discloses an uncross-linked blend of an acrylic polymer containing up to 30% polar monomers having hydroxyl, carboxylic, sulphonic acid, or phosphonic acid functionalities in combination with a polyalkyloxazoline. The increased polarity of the acrylic polymer serves to improve compatibility with the polyalkyloxazolines. A disclosed carboxylic comonomer is a carboxyethylacrylate. The polyalkyloxazoline obviates the need for cross-linking to improve cohesive strength.
U.S. Pat. No. 3,677,985 describes PSAs containing 2 to 25 percent by weight of an acrylic monomer with reactive sites such as hydroxyl or carboxyl combined with tackifying resins that also contain reactive sites and a coupling agent such as a metal salt to couple the tackifier to the resin. This tackified system does not display solvent (gasoline) resistance.
The following patents, incorporated herein by reference, deal with increased adhesion to automotive paint.
U.S. Pat. No. 4,364,972 describes an acrylic PSA containing 15 to 50% N-vinyl-2-pyrrolidone.
U.S. Pat. No. 4,726,982 describes an acrylic adhesive containing 10 to 40% N-vinyl lactam blended with a tackifying resin.
The following patents or patent disclosures, each incorporated herein by reference, relate attempts to modify pressure-sensitive adhesives in order to improve solvent resistance.
U.S. Pat. Nos. 3,718,712 and 3,767,040 disclose the use cross-linked polyurethanes and urethane cyclic terpene tackifiers.
EP 75191 describes the use of fluorinated acrylates to give good oil and water resistance.
U.S. Pat. No. 3,356,635 deals with chlorinated. elastomers combined with a urethane elastomer and a chlorinated tackifying resin.
U.S. Pat. No. 4,725,641 describes the use of polyetheresteramides and polyetheresterurethanes in rubber based adhesives to improve gasoline resistance.
U.S. Pat. No. 4,294,936 discloses blends of thermoplastic block copolymers, polyesters and tackifying resins.
None of these patents and patent disclosures disclose the use of acid functionalized acrylic monomers to increase the solvent resistance of pressure-sensitive adhesives.